Hemodialysis membranes structure

In order to solve the problems that occurred with unmodified cellulosic membranes, synthetic membranes were developed. The first synthetic polymeric membrane was produced in the early 1970s. Since that time, various synthetic polymers such as poly-sulfone, polyamide, poly(methyl methacrylate), polyethersulfone, polyethersulfone/ polyamide have been used in the production of synthetic hemodialysis membranes [20,21]. Synthetic membranes have large mean pore size and thick wall structure. These properties provide high ultrafiltration rate, which is necessary for hemodialysis to be achieved with relatively low transmembrane pressures [20]. The main difference in synthetic and cellulosic membranes is the chemical composition of the membrane. Synthetic membranes are made from manufactured thermoplastics, while both modified and unmodified cellulosic membranes are prepared from natural polymers [20]. 

Poly(31) has attracted considerable attention over the years because of practical biomedical applications such as contact lenses, coating of surgical sutures, hydrogels, and hemodialysis membranes. The success of the living anionic polymerization of protected monomers, 3 la-3 Id, opens the way to newly design well-defined amphiphilic block copolymers with more potential applications. A series of block copolymers of 31a with styrene, a-methylstyrene, 4-octylstyrene, or isoprene were synthesized and their surface structures and environmental movements were characterized in detail by TEM, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The surface reconstruction was clearly observed... 

Immunoadsorption is another way to remove middle molecules, either specifically or nonspecificaUy. Adsorptive processes can be carried out either by chemically modifying a hemodialysis membrane to create adsorption sites or by the use of an add-on device during hemodialysis. It should be mentioned that the 1 to 2-m membrane surface area on the hollow-fiber lumen is much smaller than the surface area within the porous membrane structure and may be insuBicient to provide significant toxin removal. However, one could argue that adsorptive sites within the membrane wall offer httle benefit unless significant back filtration of a toxin is taking place because it makes no difference to the patient whether a toxin is adsorbed within the membrane walls or flushed away with the spent dialysate. 

Clark WR, Hamburger RJ, Lysaght MJ. Effect of membrane composition and structure on solute removal and biocompatibility in hemodialysis. Kidney International 1999, 56, 2005-2015. 

T. Kobayashi, M. Todoki, M. Fujii, T. Takeyama and H. Tanzawa, Permeability and structure of PMMA stereocomplex hollow fiber membrane for hemodialysis, in E. Drioli and M. Nakagaki (Eds.), Proc. Eur.-fpn Cong. Membr. Membr. Processes, Plenum, New York, NY, 1986, pp. 507-513. 

The processes used to prepare cellulosic membranes generally lead to homogenous cross-sectional structures. Cellulose prepared from xanthate derivatives may exhibit a cuticle or skin structure however, this asymmetry does not produce significant resistance to mass transfer. Most membranes currently used for hemodialysis are prepared via the cuprammonlum process. These membranes do not form a skinned structure during coagulatlon/regeneratlon. 

For the design of the C-DAK 4000 artificial kidney, and the many similar hemodialysis devices (Daugirdas and Ing, 1988), rates of permeation of the species through the candidate membranes are necessary. Estimates for the permeability of pure species in a microporous membrane can be made from the molecular diffusivity, and pore diameter, porosity, and tortuosity of the membrane (Seader and Henley, 1998), as shown in Example 19.1. For this reason, considerable laboratory experimentation is required when selecting membranes in the molecular structure design step. 

The use of X-ray tomography is relatively new in the membrane field. The first experimental use of SRpCT was reported by Remigy et al. [5, 6], although Frank et al. used X-ray tomography in 2000 to observe a hemodialysis module [7]. They presented 3D reconstructed structures of UF and MF hollow fiber membranes. Yeo et al. published a paper in 2005 using X-ray microimaging (XMI) to observe the deposition of ferric hydroxide inside the fiber lumen [8] and later Chang et al. observed the flow characteristics in a hollow fiber lumen [9]. 

Capillary membranes (microporous hollow fibers) are an integral part of artificial lungs and kidneys. They represent extracorporeal applications where both the fibers and the textile structure are in direct contact with biood. For hemodialysis, mainly fibers made from cellulose, polysulfone, polymethylmethacrylate, and polyacrylonitrile are used. In oxygenators, mainly microporous hollow fibers made from polymethylpentene and silicone are used. Microporous hollow fibers can be... 

Polysulfone (PSU) is a family of thermoplastic polymers they are classified as PSU, poly(aryl sulfone), and poly(ether sulfone) (PES) by the polymer backbone structure. They are well known for their toughness and stability at high temperatures (-100°C to 150°C), high oxidative stability, and dimensional stability. Hence, it is easy to get the thin membrane with reproducible properties, which have been widely used in many fields like hemodialysis, wastewater treatment, gas separation, and especially PEM fuel cell applications. 

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